One of the greatest difficulties perceived for the development of an effective HIV vaccine is the potential for escape from protective immunity through generation of viral diversity, especially within the envelope protein. Fueling this concern is the demonstration of narrow, virus type-specific neutralizing activity when patient sera, collected during the early stages of infection, are tested against a variety of virus isolates. Although the major neutralizing determinant of the envelope surface protein gene has been identified (the "V3 loop", most of the escape-from-neutralization mutations that have been mapped to date fall outside V3, indicating that the context within which this determinant is placed is critical to its recognition. This Physician Scientist Award is intended to provide the applicant with the necessary conceptual background and laboratory training in the biology of HIV, with specific emphasis on the correlation between molecular genetic diversity and biologically-relevant, functional characteristics. It is designed to allow for the development of the applicant as an independent biomedical investigator in order to enable the pursuit of a research career as a physician-scientist. Phase I will emphasize study and research training in molecular biology, virology, and immunology. It will focus on the development and application of techniques designed to investigate the antigenic diversity of HIV-1 including the transfer of whole env genes from several HIV-1 genomes isolated directly from the blood of a single infected individual into vaccinia virus expression vectors. As part of a comprehensive study of the functional consequences of viral gene diversity, Phase II will involve the classification of the env genes in these constructs according to their neutralization susceptibility and recognition by cytotoxic T lymphocytes. Following these initial classification studies, chimeric envelope genes will be generated between antigenically divergent envelopes to map neutralization determinants and T-cell epitopes. These studies will also be expanded to other tissues from the same individual as well as from different time points when the clinical manifestation of disease has changed in order to identify determinants of tissue tropism and virulence. This approach will also be applied to a different individual whose mode of acquisition of HIV-1 differed from the individual under study. The eventual aim of these studies is to determine the antigenic diversity of virus and response to it within an individual, and to identify sites within env which control display of critical epitopes, all relevant to formulation of an effective HIV vaccine. The educational and training aspects of this proposal will also allow the applicant to gain the expertise necessary to pursue basic studies in the biology of human retroviruses, including HIV-1, as an independent investigator.